Bending Moments of an FPSO in Rogue Waves

Abstract

The increasing numbers of reported rogue waves with extreme crest and wave heights and unusual group pattern with the consequence of severe damages raise the question if such exceptional events have to be considered routinely for the design of ships and offshore structures. For the investigation of the effects of rogue wave impacts time domain simulation methods are required in addition to traditional frequency domain methods which may not be sufficient to consider these extreme events. In this paper the vertical bending moments at the midship section of an FPSO are investigated using state of the art numerical simulation tools in combination with experiments. For the seakeeping tests the extremely high New Year Wave (registered in the North Sea) is generated in the wave tank, and motions and structural forces are analyzed at model scale. For validation the results are evaluated deterministically and compared to numerical simulations. The time domain calculation allows to artificially change local wave characteristics. The steepness of the selected rogue wave is varied and the influence on wave induced loads is studied. A comparison with standard procedures of seakeeping analysis and classification rules closes the paper.

Longitudinal Forces and Bending Moments of a FPSO

“…and block coefficient of c B = 0.87. This model -with the segments connected by transverse beams for measuring the bending moments -has already been used in earlier investigations [2,3,4]. In this case, numerical and experimental results of the vertical bending moments correspond quite well if related to the waterline level.…”

Numerical and experimental analysis of extreme wave induced vertical bending moments on a FPSO

“…The FPSO being considered here has been tested in deterministic irregular wave traces including abnormal waves by Clauss et al [19] and Guedes Soares et al [11]. The agreement between calculations and experiments is good.…”

“…It is able to generate regular waves, as well as irregular seas complying with specific parametric spectra. Additionally, a procedure developed by Clauss et al [19,20] was implemented at the Laboratory to reproduce deterministic irregular wave traces at a specific target position in the tank. The method has been applied to investigate the responses of floating structures to extreme and realistic wave sequences, such as measured abnormal wave sequences [19,20,11,21].…”

“…Clauss et al [19,20] carried out experimental tests with the same model of the FPSO as presented here subjected to the NYW. Among other responses, the vertical bending moment at midship was measured.…”

Experimental and numerical study of the vertical motions of a bulk carrier and a Ro–Ro ship in extreme waves

“…The wave generator is fully computer controlled and a software is implemented which enables the generation of transient wave packages, deterministic irregular sea states with predefined characteristics as well as tailor-made critical wave sequences (Clauss and Kühnlein 1996;Clauss and Schmittner 2005). The technique has been established to reproduce a large variety of wave sequences such as single abnormal waves as well as groups of rogue waves embedded in irregular sea states to investigate the response of floating structures to an extreme, but realistic, wave environment (Clauss et al 2004).…”